The gate driver power supplies for Silicon Carbide (SiC) and Gallium Nitride (GaN) devices must meet the unique biasing requirements of these wide-bandgap semiconductors. This article discusses the key factors to consider when designing gate driver power supplies for SiC and GaN applications.
SiC and GaN are wide-bandgap (WBG) semiconductor materials that offer significant advantages over traditional silicon (Si) in power electronics applications due to their faster switching speeds and lower losses. The market share of these materials is continually increasing for applications that require high efficiency and high power density.
Early adopters vary by technology. The more mature SiC technology has largely replaced Si IGBTs for powering electric vehicle traction inverters, while GaN technology has achieved significant success in charger applications for laptops and similar devices.
Gate Driver Requirements for WBG Devices
Gate drivers for SiC and GaN transistors must be tailored to the unique characteristics of each device, particularly for high-side drivers that require isolation from their DC power supply. First-generation SiC MOSFETs typically need a gate drive voltage of +20 V for optimal on-resistance, while next-generation devices operate at +15 or +18 V and -3 or -4 V for turn-on and turn-off, respectively.
These drivers require fast rise and fall times in the nanosecond range and can handle asymmetric power supply voltages. Although power consumption rises with switching frequency, peak current is supplied by nearby capacitors, allowing for low-power DC/DC converters of 2 W to 3 W.
GaN high electron mobility transistors (HEMTs) usually require a 7 V enhancement voltage, with damage occurring at VGS above 10 V, much lower than for SiC. The low capacitance in HEMTs enables rapid switching but can cause voltage spikes due to excessive inductance in the external gate drive. A 6 V gate drive voltage effectively maintains efficiency while ensuring safety, and HEMT gates can even tolerate a turn-off voltage of zero volts.
The power supply for SiC and GaN gate drivers must deliver the appropriate voltage levels through an isolated DC/DC converter, typically providing +20/-5 V for SiC or +6 V and +9 V for GaN. Many high-side circuits operate hundreds of volts above ground, necessitating isolation for the driver and circuits. While basic isolated DC/DC converters can manage 1 kVDC for a second, this is often inadequate for high-side drivers in bridge configurations.
Therefore, the isolation voltage should be at least twice the operating voltage, as high temperatures and rapid switching impose additional stress on the isolation barrier, highlighting the need for high-isolation DC/DC converters for reliable operation.
RECOM Solutions for SiC and GaN Gate Drivers
RECOM’s DC/DC converters for gate drivers are plug-and-play modules that provide reliable and durable solutions for gate drivers in WBG applications. We offer a range of isolated DC/DC converter modules that provide simple power solutions for SiC MOSFETs or GaN HEMT power devices. These converters feature asymmetric output voltages, high isolation voltages, and low isolation capacitance.
Which RECOM DC/DC Converter Series Are Best for SiC and GaN Driver Technologies?
SiC MOSFETs: The RxxP22005D and RKZ-xx2005D series provide asymmetric output voltages of +20 V and -5 V, effectively switching SiC MOSFETs. The RxxP21503D series offers asymmetric output voltages of +15 V and -3 V for efficiently switching second-generation SiC MOSFETs.
GaN HEMTs: With RECOM's RP-xx06S and RxxP06S series DC/DC converters (which have high isolation voltages and low isolation capacitance), high-voltage slew-rate GaN transistor drivers can achieve optimal switching performance at +6 V. In GaN applications where higher noise and interference must be considered, RECOM also offers converters with +9 V output voltage, which can be divided into +6 V and -3 V using a Zener diode to provide a negative gate voltage during turn-off, ensuring that the gate voltage remains below the turn-on threshold.
RA3 Series Optimized for Gate Drivers
RECOM's RA3 series non-regulated 3 W DC/DC converters are specifically designed to power transistor gate drivers. These modules have input voltages of 5, 12, or 24 VDC and provide single or dual asymmetric outputs covering the latest Si, SiC, and GaN transistors.
The compact SMD design minimizes board space requirements, especially for multilayer PCBs. The module provides robust isolation of 5.2 kVDC/1 min and isolation capacitance of less than 10 pF. Typical efficiency ranges from 78% to 82%, and the operating temperature range at full load is from -40°C to +85°C, meeting the stringent environmental requirements for solar inverters, induction heating, telecommunications, electric vehicle battery chargers, and motor drives.
Future-Proof WBG Designs
The optimal gate driver power supply voltage combinations vary depending on the type of transistor (IGBT, SiC, or GaN), manufacturer, technology generation, and whether a common-source or common-gate configuration is used. There are some concerns within the electronics industry. How can I ensure that my design is future-proof to adapt easily to different optimal turn-on and turn-off voltages provided by future generations or alternative source transistor suppliers?
The new RECOM R24C2T25 converter addresses this challenge. This is an isolated SMD DC/DC converter in an IC-style SSOP package designed specifically for powering isolated WBG gate drivers. By using preset resistors, the regulated positive and negative output voltages can be independently adjusted within the range of +2.5 V to +22.5 V/-2.5 V to -22.5 V, allowing a single product to cover all existing gate driver voltage ranges for IGBTs, MOSFETs, SiC (all generations), and even GaN.
The output provides basic isolation levels, with an isolation voltage of 3 kVrms/1 min, and delivers 1.5 W of power across the entire operating temperature range of -40°C to +105°C without derating (up to +85°C for 2 W). The common-mode transient immunity (CMTI) exceeds 150 kV/µs, allowing the power supply to operate under extremely fast switching edges. This product comes in an SMD SSOP package, allowing for placement near the switching transistors, and comprehensive protection features (UVLO, OTP, SCP, OLP) ensure worry-free installation.
